Non-occluding intravascular blood pump providing reduced hemolysis

ABSTRACT

A non-occluding intravascular pump comprises a shroud providing an inlet for incoming blood flow and an outlet for outgoing blood flow, wherein the shroud is a cylindrical housing; an impeller positioned within shroud, wherein a central axis of the shroud and impeller are shared; a motor coupled to the impeller, wherein the motor rotates the impeller to causes blood to be drawn through the inlet and output to the outlet, and the motor is centrally disposed and shares the central axis with the shroud and the impeller; and a plurality of pillars coupling the motor to the shroud, wherein the pillars secure the shroud in close proximity to the impeller. Various design features of the pump may be optimized to reduce hemolysis, such as, but not limited to, inlet length, impeller design, pillar angle, and outlet design.

RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication No. 62/233,025 filed on Sep. 25, 2015, which is incorporatedherein by reference.

FIELD OF THE INVENTION

This invention relates to an improved non-occluding intravascular bloodpump providing reduced or minimal hemolysis.

BACKGROUND OF INVENTION

Blood pumps may exert stresses on blood that cause hemolysis or bloodclotting. A blood pump may provide an inlet, housing, impeller, outlet,and motor. There may be various hotspots in a pump's design of suchcomponents that may exert high stress on blood that can cause hemolysisor blood clotting. In addition to health risk associated with hemolysisand blood clotting, these factors may also impair operation of the bloodpump. An example of a blood pump can be found in U.S. Pat. No.8,012,079.

The improved non-occluding intravascular blood pump systems and methodsdiscussed herein reduce and minimize shear forces that can causehemolysis or blood clotting.

SUMMARY OF INVENTION

In one embodiment, a non-occluding intravascular blood pump comprises ashroud providing an inlet for incoming blood flow and an outlet foroutgoing blood flow, wherein the shroud is a cylindrical housing; animpeller positioned within shroud, wherein a central axis of the shroudand impeller are shared; a motor coupled to the impeller, wherein themotor rotates the impeller to cause blood to be drawn through the inletand output to the outlet, and the motor is centrally disposed and sharesthe central axis with the shroud and the impeller; and a plurality ofpillars coupling the motor to the shroud, wherein the pillars secure theshroud in close proximity to the impeller. The pump may further providea variety of design features to reduce hemolysis, such as, but notlimited to a trumpeted shroud with a larger inlet than outlet; rakingback the leading edge of the impeller blades; a large inlet length toreduce turbulent flow prior to the impeller; a large bare hub length;matching the pillar angle to the outlet blade angle; matching flareangles for the impeller base and stator tip; a desired clearance betweenthe shroud and impeller blades, a desired wrap angle, and anycombinations thereof.

The foregoing has outlined rather broadly various features of thepresent disclosure in order that the detailed description that followsmay be better understood. Additional features and advantages of thedisclosure will be described hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present disclosure, and theadvantages thereof, reference is now made to the following descriptionsto be taken in conjunction with the accompanying drawings describingspecific embodiments of the disclosure, wherein:

FIG. 1 shows an illustrative example of a blood pump;

FIGS. 2a-2c show multiple view of an illustrative example of a shroud;

FIGS. 3a-3c show multiple view of an illustrative example of animpeller;

FIGS. 4a-4e show multiple view of an illustrative example of a stator;

FIGS. 5a-5f show hotspots for various components of the pump;

FIG. 6 show mean/max sear stress for the shroud, blade and pillars;

FIG. 7 shows max/mean shear stress for the blade, pillars, and shroudover time;

FIG. 8 show the NIH for various rpm for P2 and P3;

FIG. 9 shows pressure rise v. NIH and measure total flow;

FIG. 10 shows the phase 2 prototype's configuration;

FIG. 11 shows an improved design with geometry data;

FIGS. 12a-12f shows selected pillar geometries;

FIGS. 13a-13f shows selected impeller geometries;

FIGS. 14a-14d show the individual components and the test surface areaevaluated for max and mean shear stress;

FIGS. 15a-15c show hydraulic output results, or more particularly,pressure rise, pump flow and shaft relative to rpm for Ref_0 and P31_30;

FIGS. 16a-16b show the maximum and mean shear stress for the referenceand P31 design

FIGS. 17a-17b show the maximum and mean shear stress for the referenceand P31 design.

FIGS. 18a-18e clearly show how the overall mean shear along the pillarscould be lowered;

FIGS. 19a-19b show the maximum and mean shear stress for the referenceand P31 design

FIG. 20 show Lagrange hemolysis estimations with Heuser constants;

FIG. 21 shows the cumulative damage index for P_Ref and P_31;

FIGS. 22a-22d illustrates the changes and improvements in shearreduction made to the impeller from P_ref to the new prototype P_31;

FIG. 23 shows a proposed prototype;

FIG. 24 shows the NIH at various rpm for prototypes; and

FIG. 25 shows the NIH v. entrainment flow for various phases of testing.

DETAILED DESCRIPTION

Refer now to the drawings wherein depicted elements are not necessarilyshown to scale and wherein like or similar elements are designated bythe same reference numeral through the several views.

Referring to the drawings in general, it will be understood that theillustrations are for the purpose of describing particularimplementations of the disclosure and are not intended to be limitingthereto. While most of the terms used herein will be recognizable tothose of ordinary skill in the art, it should be understood that whennot explicitly defined, terms should be interpreted as adopting ameaning presently accepted by those of ordinary skill in the art.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory only,and are not restrictive of the invention, as claimed. In thisapplication, the use of the singular includes the plural, the word “a”or “an” means “at least one”, and the use of “or” means “and/or”, unlessspecifically stated otherwise. Furthermore, the use of the term“including”, as well as other forms, such as “includes” and “included”,is not limiting. Also, terms such as “element” or “component” encompassboth elements or components comprising one unit and elements orcomponents that comprise more than one unit unless specifically statedotherwise.

In an improved system, the components of a non-occluding intravascularblood pump are designed to reduce or minimize hemolysis. In someembodiments, the blood pump may be a ventricular assist device or anaxial blood pump. In some embodiments, the non-occluding intravascularblood pump may provide a shroud, impeller, and flow stator.

FIG. 1 is an illustrative embodiment of a non-occluding intravascularblood pump. In some embodiments, the non-occluding intravascular bloodpump may be an axial blood pump with impeller 30 positioned within ashroud 10. Notably the central axis of the shroud 10 and impeller 30 areshared, and this central axis may be referred to as the central axis ofthe device or pump as it is shared by several components. A shroud 10may be a generally cylindrical housing for the impeller 30. The shroud10 may provide an inlet 20 for incoming blood flow and outlet foroutgoing blood flow. The device is described as intravascular because itis designed to operate in a blood vessel of the human body. In someembodiments, the central axis of the pump is roughly aligned with thecentral axis of the blood vessel. The device is non-occlusive becauseblood flowing in the blood vessel can flow freely around the device. Theimpeller 30 is coupled to and rotated by motor 40, which causes blood tobe drawn through the inlet 20 and forced out the outlet 50. The motor 40is also centrally disposed and shares the central axis with the shroud10 and impeller 30. The impeller 30 may include a hub 33 that is centralpart of the impeller. The blades or vanes 35 of the impeller 30 may beattached to the hub 33. The motor 40 may include a rotor (not shown),stator 43, and motor body 45. Because the motor 40 is centrally disposedand shares the central axis with the shroud 10 and impeller 30, outgoingblood flow from the outlet 50 is diverted around the motor 40. In orderto maintain a desired position relative to the motor 40, the shroud 10may be coupled to the motor 40 with one or more pillars 60. As the motor40 is coupled to the impeller 30, the pillars 60 may also secure theshroud 10 in close proximity to impeller. As noted previously above,there are several regions or hotspots of such a device that can createstress that may lead to hemolysis.

Further features of a non-occluding intravascular blood pump arediscussed herein for illustrative purposes. Due to the complexinteraction of various factors that influence flow it shall beunderstood that parameters discussed herein are for illustrativepurposes only and shall not be construed as limiting examples. Thus, anyparameters, such as lengths, diameters, distances, angles, or like forthe various components of the device shall be understood to benonlimiting examples, and such parameters may vary slightly from valuesdiscussed below (e.g. +/−10%). It shall also be understood that each ofthe variety of embodiments discussed herein may be suitable forcombination with one or more other embodiments.

FIGS. 2a-2c show multiple view of an illustrative example of a shroud10, more particularly, a formed shroud, an enlarged view of a strut tip,and a pre-assembled flat view respectively. In some embodiments, theshroud 10 may be integrated with struts 70 that may be utilized tosecure the device in a desired location of the circulatory system in apatient. As shown in the enlarged view of the strut tip, the tip may behook and pointed to aid secure placement (e.g. Tine bend angle=135°). Asshown in the flat view, in some embodiments, the shroud 10 may be formedby patterning (e.g. laser patterning) a desired material to providestruts 70 and pillars 60, and subsequently rolled to form the desiredcylindrical shape. The shroud material may be any suitable material(e.g. NiTi or nitinol).

In some embodiments, design aspects of the shroud 10 that are ofinterest for reducing hemolysis may include the shroud inlet shape. Insome embodiments, the shroud 10 may be trumpeted. In particular, theshroud inlet may provide a larger inlet in comparison to the outlet. Asa nonlimiting example, the shroud may be trumpeted such that an inletdiameter is larger than an outlet diameter. As discussed further below,this trumpeted design may minimize flow turbulence into the pump at theinlet.

Additionally, various parameters of the shroud 10 may also influenceperformance, including the shroud inlet length, inlet to blade anglematching, wrap angle, or combinations of these various parameters. Insome embodiments, a shroud inlet length is long enough to preventturbulent flow detachment. The shroud inlet length is defined as alength from the inlet to a tip of the impeller. In some embodiments, thenecessary length may be a function of the shroud diameter, the inletblade angle, the wrap angle, and/or impeller speed. As a nonlimitingexample, in the embodiment explored, a shroud inlet length of 9 mm orgreater was sufficient to prevent detachment. In some embodiments, ashroud inlet length of at least 1.5 times the inner diameter of theshroud is sufficient to provide good flow conditions for the impeller.In some embodiments, a shroud inlet length of at least 0.5 times theinner diameter of the shroud is included to be sufficient to providegood flow conditions for the impeller. In some embodiments, a shroudinlet length of 0.5 to 1.5 times the inner diameter of the shroud isincluded to be sufficient to provide good flow conditions for theimpeller. Optimal dimensions may depend on native flow conditions.

FIGS. 3a-3c show multiple view of an illustrative example of animpeller. More particularly, a side view, isometric view, and top viewof the impeller. As discussed previously, the impeller is positioned onthe central axis of the pump and rotates about the central axis whendriven by the motor. The hub 33 refers to the central portion of theimpeller and may be selected from any suitable blunted or truncated conedesign (e.g. spherical, elliptical, parabolic, etc.) The bare hub or hubtip 31 is a portion of the tip of the impeller before blade attachmentor a length from the tip of the hub 33 to the beginning of the blades35. The length of the hub tip 31 should be selected to providebeneficial flow results. In some embodiments, a long hub tip 31 isselected to provide laminar flow to the impeller inlet domain area. Thenecessary length and shape of the bare hub 31 may depend on the innershroud diameter, the inlet blade angle, the wrap angle, and/or impellerspeed. In some embodiments, a bare hub length of at least 0.3 times theinner diameter of the shroud may be sufficient to provide good flowmatching between the inlet flow and the impeller. In some embodiments, abare hub length of at least 0.2 times the inner diameter of the shroudmay be sufficient to provide good flow matching between the inlet flowand the impeller. In some embodiments, a bare hub length of 0.2 to 0.3times the inner diameter of the shroud may be sufficient to provide goodflow matching between the inlet flow and the impeller. In someembodiments, the bare hub length embodiments discussed herein may becombined with embodiments discussing the shroud inlet length. The inletblade angle refers to angle of the leading edge of the blade 35 relativeto the central axis when measured from the downstream side. It isapparent from figures that the leading edge is the edge of the bladeclosest to the inlet. In the embodiment explored, a bare hub length ofroughly 2 mm, with proper profiling, was sufficient to provide good flowconditions. The wrap angle refers to an angle occupied by a singleblades 35 wrapped around the hub when viewed from the perspective of thecentral axis or an angle around the central axis that the single bladeoccupies (e.g. FIG. 3c ). In some embodiments, the wrap angle may be100+/−10 degrees.

In some embodiments, the leading edges of the blades 35 may be rakedback and/or may be sharp, pointed, rounded, or the like. Traditionalpumps arrange the leading edge of vanes to extend directly perpendicularto a central axis of the pump. In other words, the leading edges of theimpeller vanes typically come straight out from the central axis of thepump or the inlet blade angle of typical impeller vanes is 90°. In someembodiments, the leading edge(s) of the impeller vanes are raked backwith respect to the direction of flow so that an inlet blade angle (orleading edge angle or rake angle) between the central axis and leadingedge is less than 90° (measured from the downstream side of the leadingedge). The proper inlet blade angle may depend on the length and shapeof the bare hub and the speed of the pump. In some embodiments, theleading edge(s) of the impeller vanes are raked back so that the leadingedge angle is ≥60° and <90°. In certain embodiments, the rake angleshould be in the range of 75-85 degrees. In some embodiments, theleading edge(s) of the impeller vanes are raked back more so that anangle between the central axis and leading edge is 60-75 degrees. Insome embodiments, the leading edge(s) of the impeller vanes are rakedback more so that an angle between the central axis and leading edge isless than 60°.

Referring to FIGS. 2a-2c and 3a-3c , the shroud and impeller may bematched. In some embodiments, the shroud-tip clearance or a clearancebetween the inner surface of the shroud and the vanes 35 of the impellermay be designed to be in a desired range. Necessary clearance values maybe related to design tolerances, the diameter of the impeller, and thespeed of the pump. As a nonlimiting example, clearances may be set tomaintain shear rates below a critical value of 10,000-50,000 s⁻¹. Forsome embodiments, the clearance distances should be at least 250 microns(+/−50 micron). In some embodiments, the clearance between the interiorsurface of the shroud and the blades of the impeller may be between 200microns to 300 microns.

FIGS. 4a-4e show multiple view of an illustrative example of a stator,which is the stationary part of a motor. In some embodiments, the statorand impeller may be matched. In some embodiments, flaring of stator hubor slope of the stator hub is selected to match the flare at the base ofthe impeller or the impeller flare angle may be approximately equal tothe stator flare angle. An impeller flare angle is an angle between theouter surface of the base of the impeller and line perpendicular to thecentral axis (e.g. FIG. 3a ). A stator flare angle is angle between theouter surface of the tip of the stator and line perpendicular to thecentral axis (e.g. FIG. 4b ). In some embodiments, the base diameter ofthe impeller and tip diameter of the stator hub may be approximatelyequal. In some embodiments, the impeller flare angle may beapproximately equal to the stator flare angle, and the base diameter ofthe impeller and tip diameter of the stator hub may be approximatelyequal. This provides a smooth transition between the impeller and statorthat minimizes disruption in flow.

Referring to FIGS. 2a-2c and 3a-3c , the pillars 60 and impeller may bematched. As shown in FIG. 2a , a pillar angle is an angle between thepillar 60 and the central axis of the pump. In some embodiments, thepillar angle is non-zero. Referring to FIG. 3a , the blade angle oroutlet blade angle is an angle of the trail end of the blade relative tothe central axis. In some embodiments, the pillars may be curved tomatch the outlet blade angle to minimize shear stress and resistance andoptimize flow path. Due to the complex interaction of various factorsthat influence flow, the optimal angle move +/−5-10 degrees from anexact matching angle.

In some embodiments, the number of pillars compared to the number ofimpeller blades may be selected to mismatch. For example, a non-integerratio of impeller blades to pillars may be selected so that they are notequal or matched. In some embodiments, the alignment of the pillarsrelative the impeller blades may be selected to mismatch, and mayoptionally combined with the above noted mismatching of the number ofpillars and blades. For example, in a nonlimiting embodiment, the pillarand blade configuration may be selected so that when at least one bladeis aligned with one of the pillars, the other remaining blades are notall aligned with the other remaining pillars. For example, three outletpillars may be provided when two impeller blades are provided. In someembodiments, the pillars may be irregularly spaced. In some embodiments,pillar and blade configurations are selected so that when at least oneblade is aligned with one of the pillars, none of the remaining impellerblades align with any of the remaining pillars.

In some embodiments, the device may be a catheter-based circulatoryheart pump, such as a pump designed specifically for NYHA Class III-IVaheart failure patients who are too sick for medication alone, but notsick enough for risky surgical interventions (i.e. LVAD or transplant).

The following examples are included to demonstrate particular aspects ofthe present disclosure. It should be appreciated by those of ordinaryskill in the art that the methods described in the examples that followmerely represent illustrative embodiments of the disclosure. Those ofordinary skill in the art should, in light of the present disclosure,appreciate that many changes can be made in the specific embodimentsdescribed and still obtain a like or similar result without departingfrom the spirit and scope of the present disclosure. It should also benoted that the examples discussed below progressed through variousphases of testing where the designs remained confidential, as suchearlier design phases should not be construed as known prior art.

Some of the challenges in producing an improved non-occludingintravascular blood pump are the numerous design factors that caninfluence performance. It was found that the best approach to get afeasible design includes seeking a minimally invasive design, highrotational speeds, and adaptation for wide operational range. Detailedflow analysis was performed, particularly transient analysis, whichallowed precise prototype comparison and setup. Further discussion belowincludes discussion of typical hotspots, geometry iterations forimpeller and housing, results, and conclusions, including hotspotanalysis that enables efficient shear force and hemolysis reduction.

The project progressed through three project phases with the initialphase starting with a basic pump design utilized to identify commondesign flaws causing hemolysis. Initial challenges of the experiments,particularly project Phase 1 and 2, were to develop hydraulic design,including ˜6 mm diameter pump, placement in the descending aorta, and inseries operation with the left ventricle. Further, additional goals wereto deliver sufficient hydraulic output to increase circulation anddecrease the workload of the native heart. Phase 3 goals includedachieving the lowest hemolysis possible, while providing a wideoff-design operating range, lower speeds, and delivering adequatehydraulic output.

Evaluation strategy included simulation in (physiological) operationenvironment with validation through pump h-q curves and pressuregradient driven backflow. Pump flow depends strongly on rpm and slightlyon output flow & pressure.

The Numerical Setup included simulation of series operation, placementin the descending aorta, pump flow function (rpm), validation of pumpperformance, hotspot analysis of impeller, including asymmetrical shearpattern, flow exploration in inflow shroud, including turbulent flowdetachment, and pillar geometry. FIGS. 5a-5f show hotspots for variouscomponents of the pump.

In order to identify the greatest potential for optimization withoutsacrificing performance, shear stress hotspot identification wasperformed. Major localized hotspots were found at the impeller, inflowshroud, and pillars. Pre-analysis included hotspot componentquantification. FIG. 6 show mean/max shear stress for the shroud, bladeand pillars. It was noted that max shear: Impeller>>Pillars>Shroud, andmean shear: Impeller˜Pillars>>Shroud. Operational range analysisincluded hotspot screening for wide operation range, particularly forconstant speed, imposed mass flows, as well as localized hotspots.

Prior to the experiments, it was unclear what provokes the asymmetricalshear pattern at the impeller leading edge. An unexpected result wasthat the detached flow reached as far as the impeller leading edge andprovoked the patterns. Transient data was also analyzed to extend theanalysis setup. FIG. 7 shows max/mean shear stress for the impeller,pillars, and shroud over time. Transient results were indispensable foroptimization, and allowed comparison of mean value and deviation fordifferent designs and identification of geometry flaws that provoketurbulent flows.

Operational range analysis was performed for hotspot screening todetermine component contribution to maximum shear stress, shear stressfor various rpms, and shear stress for impeller rotation.

Testing showed certain design features may result in improvement:

-   -   Inlet Shroud: an elongated shroud demonstrated the same        detachment and symmetric shear at impeller. A smooth inlet        transition reduced detachment length of incoming flow at the        inlet.    -   Impeller: On the upstream portion of the impeller, parameters of        interest included the bare hub length. Where the impeller blades        join the hub, parameters of interest include leading edge angle        and shape (or roundness). Along the bladed portion of the        impeller, the parameter of interest was the wrap angle (or blade        extent). At the downstream edge of the impeller blades, the        parameter of interest was the trailing edge angle or outlet        blade angle.    -   Outflow Pillars: It was found that edge shape rounding and        adjusting pillar tilt angle according to pump outflow angle were        important.

Analysis at different scales provided complimentary results. Localprediction showed improved impeller blade surface smoothness resulted ina reduction of maximum (150-200 Pa) and mean shear stress for variousRPMs. Global prediction and hotspot analysis enabled improved overallnumerically predicted damage index (include time exposure). The analysisshow overall improvement for the intended operating range.

Experimental NIH validation: FIG. 8 shows the NIH for various RPM for P2and P3, and FIG. 9 shows pressure rise v. NIH and measured total flow.Hotspot analysis enabled improved overall numerically predicted damageindex AND experimentally found levels of hemolysis. Experiments showgreatly improved hemolysis results as a multiple of BP80 referencepumps.

Conclusion: Thorough hot spot analysis to determine optimizationprocedures allows one to identify the possible interplay of hotspots,and decide on optimization order(s) to achieve a wide operation rangeand improved hydraulic output.

The non-occluding intravascular blood pump discussed herein is aminimally invasive continuous axial flow pump (e.g. ˜6 mm width) and isespecially suited for New York Heart Association (NYHA) Class III andearly IV patients. The miniaturization of a pump of this type requireshigh rotational impeller speeds to achieve sufficient unloading of theheart. In order to minimize hemolytic potential of the blood contactingcomponents, a detailed analysis was conducted and iterative optimizationof the geometry to design a prototype impeller and blood contactingcomponents. Transient computational fluid dynamic (CFD) simulations overmultiple impeller rotational speeds were conducted to determine the timedependent exposure to shear stress, shear stress hotspots, andindividual component contribution to hemolysis. The shape of the pumpcomponents were iteratively changed to optimize the local flow and shearstress exposure. The final prototype configuration was furthernumerically evaluated using a conventional Lagrange particle trackingapproach accounting for the blood damage accumulation. For validation,in vitro hemolysis testing and flow loop pump performance was conducted.Compared to the initial design, reduction in shear stress and mitigationof hotspots could be achieved. Maximum shear stress exposure could bereduced by 150-200 Pa For the impeller, and average shear on theimpeller surface was reduced below 400 Pa up to 30,000 rpm impellerspeed. Experimental results of the pump's Normalized Index of Hemolysis(NIH) values showed a significant improvement of 78% at the desiredoperating speed of 20 k rpm, showing a comparable NIH Level range as thereference pump BP80. Flow Loop performance testing verified that flowrate and pressure generation was maintained following the design changesthat resulted in reduction of hemolytic potential. The new prototypefeatures lower numerically predicted and experimentally verifiedhemolytic potential and increased efficiency through improved overallflow guidance.

In Phase III, a complete analysis of shear stress hotspots within thepump and their individual contribution to hemolysis was conducted. Themain focus of this study is the optimization towards lowest possiblehemolysis potential by iteratively adapting the blade shape.Furthermore, the whole pump is analyzed for further shear stresshotspots. After identification of the existing shortcomings in theactual prototype impeller operating at the chosen speed range, severalshroud and pillar designs are explored. A vast number of differentgeometries have been created, simulated and analyzed to determine theoptimal geometry component fit.

Current Prototype from Phase II: The current prototype (or P_ref) hasbeen identified in an extensive optimization in phase II to loweroverall hemolysis potential. FIG. 10 shows the phase 2 prototype'sconfiguration. At that time, the optimal impeller speed was determinedto be at 32 k rpm and a significant optimization could be achieved.

P_ref has been evaluated in several hemolysis tests. The main changesconducted in phase II were the iterative adaptation of inlet and outletblade angle to achieve an overall better flow guidance of the impeller,as well as an increase in wrap angle which allowed a better flowguidance within the blade passage. Furthermore, the shape of the tip hubsection has been altered to allow for a more evenly distributed andlaminar flow pattern at the impeller inlet region. In the followingdiscussion the further geometry changes to decrease the hemolyticpotential of the hotspots identified are presented.

Shroud: An efficient and reliable pump is achieved by a targeted tuningof its components to one another. A perfect example of this wasexperienced during this study. The shroud length does not significantlylower the shear stress for the component shroud, but eliminates thedependence of blade rotation angle and turbulent flow features onimpeller shear stress distribution. The extension of the shroud isnecessary to avoid detached turbulent flow reaching into the impellerinlet domain area. This turbulent flow is responsible for theasymmetrical impeller shear stress load and, due to its turbulent randomnature, impedes a significant and conclusive optimization of the blade.The results show the impact of detached flow on the shear stress valuesby having huge oscillation around its mean.

During Phase III, the shroud has therefore been extended; exact data canbe found in FIG. 6. FIG. 11 shows an improved design with geometry data.These considerations suggest that an improved pump by extending theshroud length or inlet pipe to allow for sufficient flow settlement,e.g. at least 9.3 mm for the prototype. This can be generalized as atleast 1.5 times the shroud inner diameter. Further, a trumpet shape atthe inlet is preferred in terms of even earlier flow settlement.

Pillars: The setup from FIG. 11 has been further extended to also recordstatistics for shroud and pillar stress to capture all shear stressesoccurring during 2 blade rotations. Various pillar designs have beenmodeled and simulated and are explained below. FIGS. 12a-12f showsselected pillar geometries. The basic idea behind modification of thepillar design is to align the pillars in direction of the outflow jet tominimize the surface area that is directed towards it.

Two main considerations need to be discussed. Due to the orientation ofthe pillars, the location of the hotspots is affected. A highly twistedpillar design will move the hotspot in the direction of the transitionof pillar to motor. In addition, it is assumed that a better alignedpillar compromises less attack surface area and thus reduces the averageload. Furthermore, two designs have been created. A counter orientedpillar design at 35°, as well as a stator-pillar component to assessmaximum occurring shear stress in relation to mean shear stress.

Impeller: Fifteen independent pump geometry combinations have beensimulated to identify the best possible designs and combination. FIGS.13a-13f shows selected impeller geometries. Next to the iterativeadaptation of the blade angles along the leading edge, a furtherelongation of the hub showed beneficial impact on changes made to theblade angles. Furthermore, for the same leading edge blade angles, theimpact of wrap angle has been investigated as well as a with referenceto the hub inclined leading edge.

Blood Damage Prediction: Shear-induced blood trauma (hemolysis) isestimated by computing the damage accumulation along 3000 particle pathlines using a Lagrangian particle tracking technique and applying apower-law empirical damage model as suggested by Heuser:D _(i) =C×τ ^(α) ×t ^(β)where Di represents the blood damage index for each particle, C, α and βdenote constants originally specified by Giersiepen and later correctedby Heuser asC=1.8×10⁻⁶, α=1.991, and β=0.765.

As these coefficients are derived from uniform-shear experiments inCouette-type flow, there are certain limitations to the current problem.However, it is assumed that this does not affect the comparativeevaluation of similar pumps. To account for the highly time-variantshear history of blood cells through the pump, the cumulative damage isestimated by the method extended to blood pumps by Bludszuweit (1) basedon the assumption of linear accumulation of shear at different loadinglevels:

$D_{Hb} = {\frac{1}{n}{\underset{Inlet}{\sum\limits^{Outlet}}D_{i}}}$where n is the number of total particles released in the pump inlet, andDi is calculated using the proposed constants by Heuser. Because of thethree-dimensional character of the shear field, the Von Mises stressprovides a representative scalar norm for use in calculation of D_(i),as proposed by Bludszuweit:

$\tau = \left\lbrack {{\frac{1}{6}{\sum\left( {\tau_{ii} + \tau_{jj}} \right)^{2}}} + {\sum\tau_{ij}^{2}}} \right\rbrack^{\frac{1}{2}}$where the components of the stress tensor were computed from thesummation of the components of the viscous and Reynolds stress tensor.

Results: In the course of this project, a huge data set by theevaluation of all configurations prototype was created. To anillustrative comparison, however, only the parameters of comparison ofthe original and within this project identified final pump geometry areshown below. Furthermore, most graphic results are shown at 20 krpm. Dueto the huge amount of created data, only selected configuration resultswill be shown below. The individual components and the test surface areaevaluated for max and mean shear stress are shown in FIGS. 14a-14d .Surface area K:OUTLET was monitored for every run to make sure thatmodifications made to the pillars do not somehow impair the shear stressdistribution in the whole outlet area of the pump.

A necessity for any proposed geometry modification in this study is themaintenance of sufficient hydraulic output. The modifications on theimpeller blade to achieve a lower hemolytic potential were strictlymonitored and compared to the desired hydraulic output. A small increasein hydraulic output was achieved while lowering the necessary impellershaft power. This yields in an overall better pump efficiency. FIGS.15a-15c show hydraulic output results, or more particularly, pressurerise, pump flow and shaft relative to rpm for Ref_and P31_30.

Shroud: The results for the shroud show how both maximum and mean shearstress could be lowered from the reference to the proposed design P31.FIGS. 16a-16b show the maximum and mean shear stress for the referenceand P31 design. A significant offset could be achieved.

It can be argued, that the extension of the shroud also increased thesurface area over which the mean values are derived.

Pillars: FIGS. 17a-17b show the maximum and mean shear stress for thereference and P31 design. In the case of the pillar analysis theidentification of the optimal geometry is not an obvious case. Theorientation of the pillars causes higher maximum shear stresses.Comparing the oscillation between P_REF and P_31, it can be seen thatthrough the alignment of the pillars less fluctuating events occurred.At the same time, the flow opposed surface is minimized and the overallmean shear stress could be significantly reduced. The following thetrend for P_REF, the straight pillar design might be more beneficial forhigher RPM ranges.

The following pictures depict the shear stress distribution at selectedpillar geometries. The yellow circle indicates the region of maximumoccurring shear while the blue circle covers the region of mean shear.

The charts and FIGS. 18a-18e clearly show how the overall mean shearalong the pillars could be lowered. Best results seem to be feasiblewith the 30° angle orientation of the pillar geometry.

Impeller

FIGS. 19a-19b show the maximum and mean shear stress for the referenceand P31 design. The extension of the inlet shroud and multiple designiterations including a further extension of the hub (P_17, Milestone1),improved blade angle and wrap angle extent distribution, the inclinationof the leading edge (P_22, P_26, P_31) as well as a refined rounding atthe impeller leading edge from lead to a consistent offset in bothmaximum and mean shear stress distribution comparing P_REF to P_31. Theextension of shroud could furthermore reduce the impact of detached flowand turbulence on the impeller shear stress distribution and allowed fora refined optimization.

Hemolysis Estimation

The results indicate that high hemolysis is associated with high speed.While the experiments are not an actual representation of actualhemolysis, the experiments do detect significant changes in the geometrythat lead to an overall lower shear stress distribution in the blood,and in this case, P_31 shows a lower overall hemolytic potentialcompared to P_Ref. The accumulation results have to be interpreted in acomparative manner. The absolute values should therefore be understoodmore qualitatively than quantitatively.

FIG. 20 show Lagrange hemolysis estimations with Heuser constants. FIG.21 shows the cumulative damage index for P_Ref and P_31.

Discussion

FIGS. 22a-22d illustrates the changes and improvements in shearreduction made to the impeller from P_ref to the new prototype P_31.

In milestone 1, various hemolysis hotspots were identified and thefindings allowed the extension of the current to a more advancedevaluation setup. In milestone 2 of project phase III, 15 individualpump prototypes have been simulated and analyzed over a wide range ofpump speeds.

The results of the optimization of the impeller show that a significantreduction of the maximum and mean shear stress for the investigatedoperational speed range of 18-25 k could be achieved. The combination ofimpeller P_31 with pillars that are oriented in a 30° angle combinedwith the proposed extension of inlet shroud proved to be the bestcombination among the investigated geometries. The overall pumphemolysis contribution has been investigated with a Lagrange particleapproach and could furthermore identify a clear improvement. Thepresented prototype in the current configuration therefore gives raisefor a promising perspective for future hemolysis tests.

Overall, the results clearly show that additional improvements to thereference impeller were achieved. The new prototype P_31 features lowerpredicted hemolytic potential, increased efficiency and improved overallflow guidance. FIG. 23 shows a proposed prototype.

FIG. 24 shows the NIH at various rpm for prototypes. It can be seen from20 k and 25 k that there are drastic reductions from the improveddesign. FIG. 25 shows the NIH v. entrainment flow for various phases oftesting. It can be seen that that there is a drastic change in the NIHas designs progressed through various prototype phases.

Embodiments described herein are included to demonstrate particularaspects of the present disclosure. It should be appreciated by those ofskill in the art that the embodiments described herein merely representexemplary embodiments of the disclosure. Those of ordinary skill in theart should, in light of the present disclosure, appreciate that manychanges can be made in the specific embodiments described and stillobtain a like or similar result without departing from the spirit andscope of the present disclosure. From the foregoing description, one ofordinary skill in the art can easily ascertain the essentialcharacteristics of this disclosure, and without departing from thespirit and scope thereof, can make various changes and modifications toadapt the disclosure to various usages and conditions. The embodimentsdescribed hereinabove are meant to be illustrative only and should notbe taken as limiting of the scope of the disclosure.

The invention claimed is:
 1. A non-occluding intravascular pumpcomprising: a shroud providing an inlet for incoming blood flow and anoutlet for outgoing blood flow, wherein the shroud is a cylindricalhousing, and a shroud inlet length is a length of the shroud from theinlet to a tip of an impeller, and the shroud inlet length is at least1.5 times an inner diameter of the shroud; the impeller positionedwithin the shroud, wherein a central axis of the shroud and impeller areshared, the inlet provides flow to at least two blades extending from ahub of the impeller, the blades provide a leading edge that is an edgeof the blade closest to the inlet, a leading edge angle between thecentral axis and the leading edge when measured from a downstream sideforms an angle of 75-85°; a motor coupled to the impeller, wherein themotor rotates the impeller to cause blood to be drawn through the inletand output to the outlet, and the motor is centrally disposed and sharesthe central axis with the shroud and the impeller; and a plurality ofpillars extending from one end of the outlet of the shroud toward themotor, wherein the shroud is coupled to the motor, and the shroud issecured to the motor in close proximity to the impeller.
 2. The pump ofclaim 1, wherein a diameter of the inlet is larger than a diameter ofthe outlet.
 3. The pump of claim 1, wherein an impeller flare angle isan obtuse angle between an outer conical surface of a base of theimpeller and a line perpendicular to the central axis, and the impellerflare angle is equal to a stator flare angle that is an obtuse anglebetween an outer conical surface of a tip of the motor and a lineperpendicular to the central axis.
 4. The pump of claim 1, wherein anouter impeller diameter of a base of the impeller and an outer motordiameter at a tip of the motor are equal.
 5. The pump of claim 1,wherein an impeller flare angle is an angle between an outer cylindricalsurface of a base of the impeller and a line perpendicular to thecentral axis, the flare angle is equal to a stator flare angle that isan angle between an outer cylindrical surface of a tip of a stator and aline perpendicular to the central axis, and wherein further an outerimpeller diameter of the base of the impeller and an outer motordiameter at a tip of the motor are equal.
 6. The pump of claim 1,wherein a clearance between an inner surface of the shroud and blades ofthe impeller is between 200 microns to 300 microns.
 7. The pump of claim1, wherein a hub tip length is a length of the hub from a tip of the hubto a beginning of blades on the hub of the impeller, and the hub tiplength is at least 0.3 times an inner diameter of the shroud.
 8. Thepump of claim 1, wherein a hub tip length is a length of the hub from atip of the hub to a beginning of blades on the hub of the impeller, andthe hub tip length is at least 0.3 times the inner diameter of theshroud.
 9. The pump of claim 1, wherein a wrap angle is an angle aroundthe central axis occupied by a single blade of the impeller, and thewrap angle is 100+/−10 degrees.
 10. The pump of claim 1, wherein apillar angle is an angle between the pillar and a line parallel to thecentral axis, an outlet blade angle is an angle of the trailing end ofthe blade relative to the central axis, and the outlet blade angle isequal to the pillar angle.
 11. The pump of claim 10, wherein the outletblade angle and the pillar angle are non-zero and within +/−10°.
 12. Thepump of claim 1, wherein a total number of pillars compared to a totalnumber of blades for the impeller are selected to mismatch.
 13. The pumpof claim 12, wherein the pillars and the blades are arranged so thatwhen at least one of the blade is aligned with one of the pillars,remaining blades are not all aligned with other pillars.
 14. Anon-occluding intravascular pump comprising: a shroud providing an inletfor incoming blood flow and an outlet for outgoing blood flow, whereinthe shroud is a cylindrical housing; an impeller positioned withinshroud, wherein a central axis of the shroud and impeller are shared,the inlet provides flow to a blade extending from a hub of the impeller,and the blade provides an outlet blade angle that is an angle of thetrailing end of the blade relative to the central axis; a motor coupledto the impeller, wherein the motor rotates the impeller to cause bloodto be drawn through the inlet and output to the outlet, and the motor iscentrally disposed and shares the central axis with the shroud and theimpeller; and a plurality of pillars extending from one end of theoutlet of the shroud toward the motor, wherein the shroud is coupled tothe motor, and the shroud is secured to the motor in close proximity tothe impeller, a pillar angle is an angle between the pillar and a lineparallel to the central axis, and the outlet blade angle is non-zero andwithin +/−10° the pillar angle.
 15. The pump of claim 14, wherein ashroud inlet length is a length of the shroud from the inlet to a tip ofthe impeller, and the shroud inlet length is at least 1.5 times an innerdiameter of the shroud.
 16. The pump of claim 14, wherein a hub tiplength is a length of the hub from a tip of the hub to a beginning ofblades on the hub of the impeller, and the hub tip length is at least0.3 times an inner diameter of the shroud.
 17. The pump of claim 16,wherein a wrap angle is an angle around the central axis occupied by asingle blade of the impeller, and the wrap angle is 100+/−10 degrees.18. The pump of claim 17, wherein a total number of pillars compared toa total number of blades for the impeller are selected to mismatch. 19.The pump of claim 18, wherein the pillars and the blades are arranged sothat when at least one of the blade is aligned with one of the pillars,remaining blades are not all aligned with other pillars.
 20. Anon-occluding intravascular pump comprising: a shroud providing an inletfor incoming blood flow and an outlet for outgoing blood flow, whereinthe shroud is a cylindrical housing; an impeller positioned within theshroud, wherein a central axis of the shroud and impeller are shared,the inlet provides flow to at least two blades extending from a hub ofthe impeller, the blades provide a leading edge that is an edge of theblade closest to the inlet, a leading edge angle between the centralaxis and the leading edge when measured from a downstream side forms anangle of 75-85°, wherein further an impeller flare angle is an obtuseangle between an outer conical surface of a base of the impeller and aline perpendicular to the central axis, and the impeller flare angle isequal to a stator flare angle that is an obtuse angle between an outerconical surface of a tip of a motor and a line perpendicular to thecentral axis; the motor coupled to the impeller, wherein the motorrotates the impeller to cause blood to be drawn through the inlet andoutput to the outlet, and the motor is centrally disposed and shares thecentral axis with the shroud and the impeller; and a plurality ofpillars extending from one end of the outlet of the shroud toward themotor, wherein the shroud is coupled to the motor, and the shroud issecured to the motor in close proximity to the impeller.
 21. The pump ofclaim 20, wherein a diameter of the inlet is larger than a diameter ofthe outlet.
 22. The pump of claim 20, wherein an outer impeller diameterof a base of the impeller and an outer motor diameter at a tip of themotor are equal.
 23. The pump of claim 20, wherein an outer impellerdiameter of the base of the impeller and an outer motor diameter at atip of the motor are equal.
 24. The pump of claim 20, wherein aclearance between an inner surface of the shroud and blades of theimpeller is between 200 microns to 300 microns.
 25. The pump of claim20, wherein a shroud inlet length is a length of the shroud from theinlet to a tip of the impeller, and the shroud inlet length is at least1.5 times an inner diameter of the shroud.
 26. The pump of claim 20,wherein a hub tip length is a length of the hub from a tip of the hub toa beginning of blades on the hub of the impeller, and the hub tip lengthis at least 0.3 times an inner diameter of the shroud.
 27. The pump ofclaim 20, wherein a shroud inlet length is a length of the shroud fromthe inlet to a tip of the impeller, and the shroud inlet length is atleast 1.5 times an inner diameter of the shroud, wherein further a hubtip length is a length of the hub from a tip of the hub to a beginningof blades on the hub of the impeller, and the hub tip length is at least0.3 times the inner diameter of the shroud.
 28. The pump of claim 20,wherein a wrap angle is an angle around the central axis occupied by asingle blade of the impeller, and the wrap angle is 100+/−10 degrees.29. The pump of claim 20, wherein a pillar angle is an angle between thepillar and a line parallel to the central axis, an outlet blade angle isan angle of the trailing end of the blade relative to the central axis,and the outlet blade angle is equal to the pillar angle.
 30. The pump ofclaim 29, wherein the outlet blade angle and the pillar angle arenon-zero and within +/−10°.
 31. The pump of claim 20, wherein a totalnumber of pillars compared to a total number of blades for the impellerare selected to mismatch.
 32. The pump of claim 31, wherein the pillarsand the blades are arranged so that when at least one of the blade isaligned with one of the pillars, remaining blades are not all alignedwith other pillars.